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[Text] / N. V. Erkaev [et al.] // Astrobiology. - 2013. - Vol. 13, Is. 11. - P1011-1029, DOI 10.1089/ast.2012.0957. - Cited References: 92. - M. Gudel, K. G. Kislyakova, M. L. Khodachenko, and H. Lammer acknowledge support by the FWF NFN project S116 601-N16 "Pathways to Habitability: From Disks to Active Stars, Planets and Life" and the related FWF NFN subprojects S116 604-N16 "Radiation & Wind Evolution from T Tauri Phase to ZAMS and Beyond," S116 606-N16 "Magnetospheric Electrodynamics of Exoplanets," S116 607-N16 "Particle/Radiative Interactions with Upper Atmospheres of Planetary Bodies under Extreme Stellar Conditions." K. G. Kislyakova, Yu. N. Kulikov, H. Lammer, and P. Odert thank also the Helmholtz Alliance project "Planetary Evolution and Life." P. Odert and A. Hanslmeier also acknowledge support from the FWF project P22950-N16. The authors also acknowledge support from the EU FP7 project IMPEx (No. 262863) and the EUROPLANET-RI projects, JRA3/EMDAF and the Na2 science WG5. The authors thank the International Space Science Institute (ISSI) in Bern and the ISSI team "Characterizing stellar and exoplanetary environments." N. V. Erkaev acknowledges support by the RFBR grant No 12-05-00152-a. Finally, the authors thank referee Tian Feng, from the Tsinghua University, Beijing, China, for suggestions and recommendations that helped to improve the work. . - 19. - ISSN 1531-1074РУБ Astronomy & Astrophysics + Biology + Geosciences, Multidisciplinary

Аннотация: The recently discovered low-density super-Earths Kepler-11b, Kepler-11f, Kepler-11d, Kepler-11e, and planets such as GJ 1214b represent the most likely known planets that are surrounded by dense H/He envelopes or contain deep H2O oceans also surrounded by dense hydrogen envelopes. Although these super-Earths are orbiting relatively close to their host stars, they have not lost their captured nebula-based hydrogen-rich or degassed volatile-rich steam protoatmospheres. Thus, it is interesting to estimate the maximum possible amount of atmospheric hydrogen loss from a terrestrial planet orbiting within the habitable zone of late main sequence host stars. For studying the thermosphere structure and escape, we apply a 1-D hydrodynamic upper atmosphere model that solves the equations of mass, momentum, and energy conservation for a planet with the mass and size of Earth and for a super-Earth with a size of 2 R-Earth and a mass of 10 M-Earth. We calculate volume heating rates by the stellar soft X-ray and extreme ultraviolet radiation (XUV) and expansion of the upper atmosphere, its temperature, density, and velocity structure and related thermal escape rates during the planet's lifetime. Moreover, we investigate under which conditions both planets enter the blow-off escape regime and may therefore experience loss rates that are close to the energy-limited escape. Finally, we discuss the results in the context of atmospheric evolution and implications for habitability of terrestrial planets in general. Key Words: Stellar activityLow-mass starsEarly atmospheresEarth-like exoplanetsEnergetic neutral atomsIon escapeHabitability. Astrobiology 13, 1011-1029.

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Держатели документа:
[Erkaev, Nikolai V.] Russian Acad Sci, Siberian Div, Inst Computat Modelling, Krasnoyarsk 660036, Russia
[Erkaev, Nikolai V.] Siberian Fed Univ, Krasnoyarsk, Russia
[Lammer, Helmut
Odert, Petra
Kislyakova, Kristina G.
Khodachenko, Maxim L.
Biernat, Helfried] Austrian Acad Sci, Space Res Inst, A-8010 Graz, Austria
[Odert, Petra
Kislyakova, Kristina G.
Hanslmeier, Arnold] Graz Univ, Inst Phys, Graz, Austria
[Kulikov, Yuri N.] Russian Acad Sci, Polar Geophys Inst, Murmansk, Russia
[Khodachenko, Maxim L.] Moscow MV Lomonosov State Univ, Inst Nucl Phys, Moscow, Russia
[Guedel, Manuel] Univ Vienna, Inst Astrophys, A-1010 Vienna, Austria
ИВМ СО РАН

Доп.точки доступа:
Erkaev, N.V.; Еркаев, Николай Васильевич; Lammer, H.; Odert, P.; Kulikov, Y.N.; Kislyakova, K.G.; Khodachenko, M.L.; Gudel, M.; Hanslmeier, A.; Biernat, H.K.; FWF NFN project [S116 601-N16, S116 604-N16, S116 606-N16, S116 607-N16]; FWF project [P22950-N16]; EU [262863]; EUROPLANET-RI projects; JRA3/EMDAF; Na2 science WG5; RFBR [12-05-00152-a]

/ K. G. Kislyakova [et al.] // Astrobiology. - 2013. - Vol. 13, Is. 11. - P1030-1048, DOI 10.1089/ast.2012.0958 . - ISSN 1531-1074
Аннотация: We studied the interactions between the stellar wind plasma flow of a typical M star, such as GJ 436, and the hydrogen-rich upper atmosphere of an Earth-like planet and a "super-Earth" with a radius of 2 R Earth and a mass of 10 MEarth, located within the habitable zone at ∼0.24 AU. We investigated the formation of extended atomic hydrogen coronae under the influences of the stellar XUV flux (soft X-rays and EUV), stellar wind density and velocity, shape of a planetary obstacle (e.g., magnetosphere, ionopause), and the loss of planetary pickup ions on the evolution of hydrogen-dominated upper atmospheres. Stellar XUV fluxes that are 1, 10, 50, and 100 times higher compared to that of the present-day Sun were considered, and the formation of high-energy neutral hydrogen clouds around the planets due to the charge-exchange reaction under various stellar conditions was modeled. Charge-exchange between stellar wind protons with planetary hydrogen atoms, and photoionization, lead to the production of initially cold ions of planetary origin. We found that the ion production rates for the studied planets can vary over a wide range, from ∼1.0×1025 s-1 to ∼5.3×1030 s-1, depending on the stellar wind conditions and the assumed XUV exposure of the upper atmosphere. Our findings indicate that most likely the majority of these planetary ions are picked up by the stellar wind and lost from the planet. Finally, we estimated the long-time nonthermal ion pickup escape for the studied planets and compared them with the thermal escape. According to our estimates, nonthermal escape of picked-up ionized hydrogen atoms over a planet's lifetime within the habitable zone of an M dwarf varies between ∼0.4 Earth ocean equivalent amounts of hydrogen (EOH) to <3 EOH and usually is several times smaller in comparison to the thermal atmospheric escape rates. © 2013 Mary Ann Liebert, Inc.

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Держатели документа:
Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, A-8042 Graz, Austria
Institute of Physics, University of Graz, Graz, Austria
Swedish Institute of Space Physics, Kiruna, Sweden
Institute of Computational Modelling, Siberian Division of the Russian Academy of Sciences, Krasnoyarsk, Russian Federation
SINP, Moscow State University, Moscow, Russian Federation
Polar Geophysical Institute (PGI), Russian Academy of Sciences, Murmansk, Russian Federation
Institute of Astrophysics, University of Vienna, Austria
ИВМ СО РАН

Доп.точки доступа:
Kislyakova, K.G.; Lammer, H.; Holmstrom, M.; Panchenko, M.; Odert, P.; Erkaev, N.V.; Еркаев, Николай Васильевич; Leitzinger, M.; Khodachenko, M.L.; Kulikov, Y.N.; Gudel, M.; Hanslmeier, A.

[Text] / H. . Lammer [et al.] // Astrobiology. - 2007. - Vol. 7, Is. 1. - P185-207, DOI 10.1089/ast.2006.0128. - Cited References: 104 . - ISSN 1531-1074РУБ Astronomy & Astrophysics + Biology + Geosciences, Multidisciplinary

Аннотация: Atmospheric erosion Of CO2-rich Earth-size exoplanets due to coronal mass ejection (CME)-induced ion pick up within close-in habitable zones of active M-type dwarf stars is investigated. Since M stars are active at the X-ray and extreme ultraviolet radiation (XUV) wavelengths over long periods of time, we have applied a thermal balance model at various XUV flux input values for simulating the thermospheric heating by photodissociation and ionization processes due to exothermic chemical reactions and cooling by the CO2 infrared radiation in the 15 mu m band. Our study shows that intense XUV radiation of active M stars results in atmospheric expansion and extended exospheres. Using thermospheric neutral and ion densities calculated for various XUV fluxes, we applied a numerical test particle model for simulation of atmospheric ion pick up loss from an extended exosphere arising from its interaction with expected minimum and maximum CME plasma flows. Our results indicate that the Earth-like exoplanets that have no, or weak, magnetic moments may lose tens to hundreds of bars of atmospheric pressure, or even their whole atmospheres due to the CME-induced O+ ion pick up at orbital distances <= 0.2 astronomical units. We have found that, when exposed to intense XUV fluxes, atmospheres with CO2/N-2 mixing ratios lower than 96% will show an increase in exospheric temperatures and expanded thermosphere-exosphere environments. Hence, they suffer stronger atmospheric erosion, which can result in the total loss of several hundred bars even if an exoplanet is protected by a "magnetic shield" with its boundary located at I Earth radius above the surface. Furthermore, our study indicates that magnetic moments of tidally locked Earth-like exoplanets are essential for protecting their expanded upper atmospheres because of intense XUV radiation against CME plasma erosion. Therefore, we suggest that larger and more massive terrestrial-type exoplanets may better protect their atmospheres against CMEs, because the larger cores of such exoplanets would generate stronger magnetic moments and their higher gravitational acceleration would constrain the expansion of their thermosphere-exosphere regions and reduce atmospheric escape.


Доп.точки доступа:
Lammer, H.; Lichtenegger, H.I.M.; Kulikov, Y.N.; Griessmeier, J.M.; Terada, N.; Erkaev, N.V.; Еркаев, Николай Васильевич; Biernat, H.K.; Khodachenko, M.L.; Ribas, I.; Penz, T.; Selsis, F.

[Text] / H. Lammer [et al.] // Celest. Mech. Dyn. Astron. - 2005. - Vol. 92, Is. 01.03.2013. - P273-285, DOI 10.1007/s10569-005-0004-4. - Cited References: 27 . - ISSN 0923-2958РУБ Astronomy & Astrophysics + Mathematics, Interdisciplinary Applications

Аннотация: The region around a star where a life-supporting biosphere can evolve is the so-called Habitable Zone (HZ). The current definition of the HZ is based only on the mass-luminosity relation of the star and climatological and meteorological considerations of Earth-like planets, but neglects atmospheric loss processes due to the interaction with the stellar radiation and particle environment. From the knowledge of the planets in the Solar System, we know that planets can only evolve into a habitable world if they have a stable orbit around its host star and if they keep the atmosphere and water inventory during: (i) the period of heavy bombardment by asteroids and comets and (ii) during the host stars' active X-ray and extreme ultraviolet (XUV) and stellar wind periods. Impacts play a minor role for planets with the size and mass like Earth, while high XUV fluxes and strong stellar winds during the active periods of the young host star can destroy the atmospheres and water inventories. We show that XUV produced temperatures in the upper atmospheres of Earth-like planets can lead to hydrodynamic "blow off", resulting in the total loss of the planets water inventory and atmosphere, even if their orbits lie inside the HZ. Further, our study indicates that Earth-like planets inside the HZ of low mass stars may not develop an atmosphere, because at orbital distances closer than 0.3 AU, their atmospheres are highly affected by strong stellar winds and coronal mass ejections (CME's). Our study suggests that planetary magnetospheres will not protect the atmosphere of such planets, because the strong stellar wind of the young star can compress the magnetopause to the atmospheric obstacle. Moreover, planets inside close-in HZ's are tidally locked, therefore, their magnetic moments are weaker than those of an Earth-like planet at 1 AU. Our results indicate that Earth-like planets in orbits of low mass stars may not develop stable biospheres. From this point of view, a HZ, where higher life forms like on Earth may evolve is possibly restricted to higher mass K stars and G stars.


Доп.точки доступа:
Lammer, H.; Kulikov, Y.N.; Penz, T.; Leitner, M.; Biernat, H.K.; Erkaev, N.V.; Еркаев, Николай Васильевич

/ H. Lammer [et al.] // Origins of Life and Evolution of Biospheres. - 2014. - Vol. 44, Iss. 3. - P239-260, DOI 10.1007/s11084-014-9377-2 . - ISSN 0169-6149
Аннотация: We study the origin and escape of catastrophically outgassed volatiles (H2O, CO2) from exomoons with Earth-like densities and masses of 0.1, 0.5 and 1 M? orbiting an extra-solar gas giant inside the habitable zone of a young active solar-like star. We apply a radiation absorption and hydrodynamic upper atmosphere model to the three studied exomoon cases. We model the escape of hydrogen and dragged dissociation products O and C during the activity saturation phase of the young host star. Because the soft X-ray and EUV radiation of the young host star may be up to ~100 times higher compared to today’s solar value during the first 100 Myr after the system’s origin, an exomoon with a mass < 0.25 M? located in the HZ may not be able to keep an atmosphere because of its low gravity. Depending on the spectral type and XUV activity evolution of the host star, exomoons with masses between ~0.25 and 0.5 M? may evolve to Mars-like habitats. More massive bodies with masses >0.5 M?, however, may evolve to habitats that are a mixture of Mars-like and Earth-analogue habitats, so that life may originate and evolve at the exomoon’s surface.

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Доп.точки доступа:
Lammer, H.; Schiefer, S.-C.; Juvan, I.; Odert, P.; Erkaev, N.V.; Еркаев, Николай Васильевич; Weber, C.; Kislyakova, K.G.; Gudel, M.; Kirchengast, G.; Hanslmeier, A.

/ H. Lammer [et al.] // The Early Evolution of the Atmospheres of Terrestrial Planets. - New York : Springer, 2013. - pp. 33-52. - (Astrophysics and Space Science Proceedings) . - ISBN 978-1-4614-5190-7


Доп.точки доступа:
Lammer, H.; Kislyakova, K.G.; Gudel, M.; Holmstrom, M.; Erkaev, N.V.; Еркаев, Николай Васильевич; Odert, P.; Khodachenko, M.L.

/ P. E. Cubillos [et al.] // Astrophys. J. - 2017. - Vol. 849, Is. 2, DOI 10.3847/1538-4357/aa9019 . - ISSN 0004-637X
Аннотация: The strong, nearly wavelength-independent absorption cross section of aerosols produces featureless exoplanet transmission spectra, limiting our ability to characterize their atmospheres. Here, we show that even in the presence of featureless spectra, we can still characterize certain atmospheric properties. Specifically, we constrain the upper and lower pressure boundaries of aerosol layers, and present plausible composition candidates. We study the case of the bloated Saturn-mass planet WASP-49 b, where near-infrared observations reveal a flat transmission spectrum between 0.7 and 1.0 ?m. First, we use a hydrodynamic upper-atmosphere code to estimate the pressure reached by the ionizing stellar high-energy photons at 10-8 bar, setting the upper pressure boundary where aerosols could exist. Then, we combine HELIOS and Pyrat Bay radiative-transfer models to constrain the temperature and photospheric pressure of atmospheric aerosols, in a Bayesian framework. For WASP-49 b, we constrain the transmission photosphere (hence, the aerosol deck boundaries) to pressures above 10-5 bar (100?solar metallicity), 10-4 bar (solar), and 10-3 bar (0.1?solar) as the lower boundary, and below 10-7 bar as the upper boundary. Lastly, we compare condensation curves of aerosol compounds with the planet's pressure-temperature profile to identify plausible condensates responsible for the absorption. Under these circumstances, we find these candidates: Na2S (at 100? solar metallicity); Cr and MnS (at solar and 0.1?solar); and forsterite, enstatite, and alabandite (at 0.1?solar). © 2017. The American Astronomical Society. All rights reserved.

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Держатели документа:
Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, Graz, Austria
Federal Research Center Krasnoyarsk Science Center SB RAS, Institute of Computational Modelling, Krasnoyarsk, Russian Federation
Center for Space and Habitability, University of Bern, Sidlerstrasse 5, Bern, Switzerland
Institut fur Geophysik und Meteorologie, Universitat zu Koln, Albertus-Magnus-Platz, Koln, Germany
Max Planck Institute for Astronomy, Konigstuhl 17, Heidelberg, Germany
Department of Astrophysics, University of Vienna, Turkenschanzstrasse 17, Vienna, Austria
Geneva Observatory, University of Geneva, ch. de Maillettes 51, Versoix, Switzerland

Доп.точки доступа:
Cubillos, P. E.; Fossati, L.; Erkaev, N. V.; Malik, M.; Tokano, T.; Lendl, M.; Johnstone, C. P.; Lammer, H.; Wyttenbach, A.